In a Long Term Evolution (LTE) system, a radio frame is divided into ten sub-frames, the length of each sub-frame is 1 millisecond (ms). Seven TDD uplink/downlink configurations are defined for a radio frame of a Time Division Duplex (TDD) system. As depicted in Table 1, D represents a downlink sub-frame, U represents an uplink sub-frame, and S represents a special sub-frame of the TDD system. The special sub-frame is composed of three components including a Downlink Pilot Time Slot (DwPTS), a Guard Period (GP) and an Uplink Pilot Time Slot (UpPTS).
TABLE 1Uplink/Switchingdownlinkperiodicityconfigura-of downlinkSub-frame indextionto uplink012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
Compared with the LTE system, Long Term Evolution-Advanced (LTE-A) system has significantly improved system peak data rates, which requires up to 1 Gbps in the downlink and 500 Mbps in the uplink. Thus a bandwidth available to a User Equipment (UE) (also referred to as a terminal) needs to be extended in the LTE-A system, that is, a plurality of consecutive or inconsecutive carriers served by the same evolved Node B (eNB) are aggregated together to serve the UE concurrently. These carriers aggregated together are referred to as Component Carriers (CCs). Each cell can be a component carrier, and the bandwidth of each component carrier is no larger than 20 MHz to ensure backward compatibility with the LTE system.
Intra-band carrier aggregation (CA) and inter-band carrier aggregation can be applicable dependent upon the bands where the aggregated carriers are located. In the Release-11 (Rel-11) and releases subsequent thereto, a UE in a system with carrier aggregation can share or access an adjacent band with another system. As illustrated in FIG. 1, three carriers are aggregated for the UE, where the carrier 1 and the carrier 2 are located in the band 1 and the carrier 3 is located in the band 2. In order to avoid uplink/downlink cross interference between the adjacent TDD systems, the UE shall use an uplink/downlink configuration on the carrier 1 and the carrier 2 which can coexist with the adjacent 3G/LTE TDD system in the band A, and the UE shall use an uplink/downlink configuration on the carrier 3 which can coexist with the adjacent 3G/LTE TDD system in the band B. The so-called “coexist” refers to a configuration without uplink/downlink cross interference; for the LTE system, it refers to the same TDD uplink/downlink configuration. When the LTE system operates in the band A and the band B respectively with different TDD uplink/downlink configurations, the TDD uplink/downlink configuration of the carriers 1 and 2 is different from that of the carrier 3, that is, the carriers which have different TDD uplink/downlink configurations are aggregated for the UE.
The LTE-A UE needs to feed back Acknowledgment/Non-Acknowledgment (ACK/NACK) feedback information of a plurality of carriers (such as carriers of a TDD system and downlink carriers of a Frequency Division Duplex (FDD) system) and downlink sub-frames (where a special sub-frame is also considered as a downlink sub-frame because downlink data is transmitted in the DwPTS in the special sub-frame) in the same uplink sub-frame. The number of downlink sub-frames on a carrier for which ACK/NACK is fed back in the same sub-frame is defined as M, where the value of M differs from one uplink sub-frame to another and one TDD uplink/downlink configuration to another. Thus the value of M can be determined by the number of sub-frames in a set of downlink sub-frames associated with an uplink sub-frame in a corresponding TDD uplink/downlink configuration. The set of downlink sub-frames is composed of downlink sub-frames n-k associated with an uplink sub-frame n, where kε a set of indexes K. For the different TDD uplink/downlink configurations, the values in the set of index K are as depicted in Table 2. In Table 2, for the respective TDD uplink/downlink configurations, each uplink sub-frame n corresponds respectively to a set of indexes K={k0, k1, . . . kM-1}. Particularly for special sub-frames with a downlink normal Cyclic Prefix (CP) and corresponding to special sub-frame configurations 0 and 5 and special sub-frames with a downlink extended CP and corresponding to special sub-frame configurations 0 and 4, no ACK/NACK is fed back for these special sub-frames. In other words, when the set of downlink sub-frames corresponding to the uplink sub-frame n includes the special sub-frames with a downlink normal CP and corresponding to special sub-frame configurations 0 and 5 and/or the special sub-frames with a downlink extended CP and corresponding to special sub-frame configurations 0 and 4, M represents the number of downlink sub-frames other than the special sub-frames in the set of downlink sub-frames corresponding to the uplink sub-frame n; otherwise, M represents the number of all the downlink sub-frames in the set of downlink sub-frames associated with the uplink sub-frame n.
TABLE 2Uplink/downlinkconfigura-Sub-frame numbertion01234567890——6—4——6—41——7, 64———7, 64—2——8, 7,————8, 7,——4, 64, 63——7, 6,6, 55, 4—————114——12, 8,6, 5,——————7, 114, 75——13, 12,———————9, 8,7, 5,4, 11,66——775——77—
Table 2 only depicts the relationship between the uplink sub-frame and the set of indexes K in a radio frame as an example, where n−k<0 represents a sub-frame in a preceding radio frame.
In the Rel-11, transmission of a Physical Uplink Control Channel (PUCCH) is only supported on a Primary Component Carrier (PCC). A downlink Hybrid Automatic Repeat reQuest (HARQ) timing relationship (simply DL HARQ timing) of the PCC is determined by a TDD uplink/downlink configuration notified to the PCC in a System Information Block (SIB) 1. The so-called DL HARQ timing refers to a relationship between a sub-frame (a downlink sub-frame or a special sub-frame) on a carrier and an uplink sub-frame in which ACK/NACK feedback information of the sub-frame is transmitted. When TDD uplink/downlink configurations, notified in the SIB1's corresponding to the respective carriers aggregated for the UE, are different, in order to feed back the ACK/NACK of a Secondary Component Carrier (SCC), that is, in order to locate an uplink sub-frame on the PCC in which ACK/NACK of a downlink sub-frame on the SCC is transmitted, DL HARQ timing of the SCC needs to be determined from a reference TDD uplink/downlink configuration, where the reference TDD uplink/downlink configuration may be a TDD uplink/downlink configuration notified to the SCC or the PCC in the SIB1 or an existing TDD uplink/downlink configuration other than the TDD uplink/downlink configuration above.
In the scenario above, when ACK/NACK is transmitted on a Physical Uplink Shared Channel (PUSCH), for a PUSCH without any corresponding Physical Downlink Control Channel (PDCCH), the number of ACK/NACK bits of a carrier c carried in the current uplink sub-frame n can be determined from BcDL, where BcDL=Mc, BcDL represents the number of downlink sub-frames on the carrier c for which ACK/NACK needs to be fed back in the current uplink sub-frame n, and Mc represents a value determined from the number of downlink sub-frames in the set of downlink sub-frames on the carrier c associated with the current uplink sub-frame n, and the set of downlink sub-frames is composed of the downlink sub-frames on the carrier c determined from the set of indexes K associated with the current uplink sub-frame n indicated by the reference TDD uplink/downlink configuration of the carrier c.
However there is no a specific solution to determine BcDL of each carrier yet in other scenarios, e.g., a scenario where a PUSCH has a corresponding PDCCH.